Method for detecting a clear path through topographical variation analysis

ABSTRACT

A method for detecting a clear path of travel for a vehicle wherein the detecting includes a fusion of a plurality of analyses including monitoring an image from a camera device includes analyzing the image through clear path detection analysis to determine a clear path of travel within the image, analyzing an area in front of the vehicle utilizing a topographical variation analysis to determine a flat surface upon which the vehicle can travel, combining the clear path of travel and the determined flat surface to describe an enhanced clear path of travel, and utilizing the enhanced clear path of travel to navigate the vehicle.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 12/581,659 filed on Oct. 19, 2009, which is a continuation-in-part of U.S. application Ser. No. 12/474,594 filed on May 29, 2009, which is a continuation-in-part of U.S. application Ser. No. 12/108,581 filed on Apr. 24, 2008. U.S. application Ser. No. 12/581,659 filed on Oct. 19, 2009 claims the benefit of U.S. Provisional Application 61/215,745 filed on May 8, 2009. U.S. application Ser. No. 12/581,659, U.S. application Ser. No. 12/474,594, U.S. application Ser. No. 12/108,581, and U.S. Provisional Application 61/215,745 are incorporated herein by reference.

TECHNICAL FIELD

This disclosure is related to automated or semi-automated control of a motor vehicle.

BACKGROUND

The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

Autonomous driving systems and semi-autonomous driving systems utilize inputs regarding the road and other driving conditions to automatically control throttle and steering mechanisms. Accurate estimation and identification of a clear path over which to operate a motor vehicle is critical to successfully replacing the human mind as a control mechanism for vehicle operation.

Road conditions can be complex. Under normal operation of a vehicle, the human operator makes hundreds of observations per minute and adjusts operation of the vehicle on the basis of perceived road conditions. One aspect of perceiving road conditions is the perception of the road in the context of objects in and around the roadway and navigating a clear path through any objects. Replacing human perception with technology preferentially includes some means to accurately perceive objects, for example, including stationary objects such as roadside curbs and moving objects such as other vehicles, and road conditions, such as lane markers, potholes, or icy patches upon the roadway, and continue to effectively navigate around such navigational concerns.

Technological means for perceiving an object or road conditions include data from visual cameras, radar imaging, LIDAR, vehicle to vehicle communications, vehicle to infrastructure communications, and use of global positioning data with a digital map. Cameras translate visual images in the form of radiation such as light patterns or infrared signatures into a readable data format. One such data format includes pixelated images, in which a perceived scene is broken down into a series of pixels. Radar imaging utilizes radio waves generated by a transmitter to estimate shapes and objects present in front of the transmitter. Patterns in the waves reflecting off these shapes and objects can be analyzed and the locations of objects can be estimated.

Once data has been generated regarding the ground in front of the vehicle, the data must be analyzed to estimate the presence of objects or road conditions from the data. By using cameras and radar imaging systems, ground or roadway in front of the vehicle can be analyzed for the presence of objects or road conditions that might need to be avoided. However, the mere identification of potential navigational concerns to be avoided does not complete the analysis. An important component of any autonomous system includes how potential navigational concerns identified in perceived ground data are processed and manipulated to identify a clear path in which to operate the vehicle.

One known method to identify a clear path in which to operate the vehicle is to catalog and provisionally identify all perceived navigational concerns and identify a clear path in light of the locations and behaviors of identified concerns. Images may be processed to identify and classify navigational concerns according to their form and relationship to the roadway. While this method can be effective in identifying a clear path, it requires a great deal of processing power, for example, requiring the recognition and separation of different objects in the visual image, for instance, distinguishing between a tree along the side of the road and a pedestrian walking toward the curb. Such methods can be slow or ineffective to process complex situations or may require bulky and expensive equipment to supply the necessary processing capacity.

SUMMARY

A method for detecting a clear path of travel for a vehicle wherein the detecting includes a fusion of a plurality of analyses including monitoring an image from a camera device includes analyzing the image through clear path detection analysis to determine a clear path of travel within the image, analyzing an area in front of the vehicle utilizing a topographical variation analysis to determine a flat surface upon which the vehicle can travel, combining the clear path of travel and the determined flat surface to describe an enhanced clear path of travel, and utilizing the enhanced clear path of travel to navigate the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 illustrates an exemplary arrangement of a vehicle equipped with a camera and a radar imaging system in accordance with the present disclosure;

FIG. 2 illustrates a known method to determine a clear path for autonomous driving in accordance with the present disclosure;

FIG. 3 illustrates an exemplary method to determine a clear path utilizing a likelihood analysis of an image in accordance with the present disclosure;

FIG. 4 illustrates an exemplary method to analyze an image in accordance with the present disclosure;

FIG. 5 illustrates an exemplary method to define a classification error by tuning a single threshold in accordance with the present disclosure;

FIGS. 6A, 6B, and 6C illustrate an exemplary determination of an image difference by calculating an absolute image intensity difference in accordance with the present disclosure;

FIG. 7 illustrates an exemplary method to classify a feature as a portion of a clear path and as a detected object at the same time as a method of image analysis in accordance with the present disclosure;

FIG. 8 further illustrates an exemplary method to classify a feature as a portion of a clear path and as a detected object at the same time as a method of image analysis in accordance with the present disclosure;

FIG. 9 is a flowchart for an exemplary patch-based method for detecting a clear path in accordance with the present disclosure;

FIG. 10 is a flowchart for a texture-rich pixel-based method for detecting a clear path, in accordance with the present disclosure;

FIG. 11 is a flowchart for a textureless pixel-based method for detecting a clear path, in accordance with the present disclosure;

FIG. 12 shows the vehicle with respect to ground during vehicle travel including different camera perspectives of identified features, in accordance with the present disclosure;

FIG. 13 shows the camera relative to a ground plane in accordance with the present disclosure;

FIG. 14 graphically depicts exemplary operation of clear path analysis, snow elevation detection, and ground plane estimation, in accordance with the present disclosure;

FIGS. 15A and 15B show an exemplary image including exemplary image areas for analysis using a snow elevation change detection analysis, in accordance with the present disclosure;

FIG. 16 is a flowchart for an exemplary method for augmenting the clear path detection analysis with detected snow elevation changes and an estimated ground plane, in accordance with the present disclosure; and

FIG. 17 graphically depicts an exemplary iterative analysis, in accordance with the present disclosure.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same, FIG. 1 illustrates an exemplary arrangement of camera 110 located on the front of a vehicle 100 and pointed toward the ground in front of the vehicle 100 in accordance with the present disclosure. Camera 110 is in communication with processing module 120 containing logic to process inputs from camera 110. The vehicle 100 may also be equipped with a radar imaging system 130, which, when present, is also in communication with processing module 120. It should be appreciated by those having ordinary skill in the art that the vehicle 100 could utilize a number of methods to identify road conditions in addition or in the alternative to the use of camera 110 and the radar imaging system 130, including GPS information, information from other vehicles in communication with the vehicle 100, historical data concerning the particular roadway, biometric information such as systems reading the visual focus of the driver, a radar imaging system, or other similar systems. The disclosure herein can be applied to various device arrangements and is therefore not limited thereby.

The camera 110 is a device well known in the art capable of translating visual inputs in the form of light, infrared, or other electro-magnetic (EM) radiation into a data format readily capable of analysis, e.g., a digital, pixelated image. In one embodiment, the camera 110 uses a charge coupled device (CCD) sensor to generate images indicating a field-of-view. Preferably, the camera 110 is configured for continuous image generation, e.g., 30 images generated per second. Images generated by the camera 110 may be stored in memory within the camera 110 or transferred to the processing module 120 for storage and/or analysis. Preferably, each image generated by the camera 110 is a two-dimensional image of known pixel dimensions comprising a plurality of identifiable pixels. The plurality of identifiable pixels may be stored and analyzed using an array. Each pixel may be represented in the array as a set of bits or a plurality of sets of bits wherein the bits correspond to a color on a predetermined palette or color map. Each pixel may be expressed as a function of a plurality of color intensity values such as in a red-green-blue (RGB) color model or a cyan-magenta-yellow-key (CMYK) color model. Preferably, each pixel comprises a plurality of sets of bits wherein each set of bits corresponds to a color intensity and a color intensity value e.g., a first set of bits corresponds to a red color intensity value, a second set of bits corresponds to a green color intensity value, and a third set of bits corresponds to blue color intensity value on the RGB color model.

The radar imaging device 130 is a device well known in the art incorporating a transmitter capable of emitting radio waves or other EM radiation, a receiver device capable of sensing the emitted waves reflected back to the receiver from objects in front of the transmitter, and means to transfer the sensed waves into a data format capable of analysis, indicating for example range and angle from the objects off which the waves reflected. Alternatively, the radar imaging device 130 may be replaced or supplemented with a light detection and ranging (LIDAR) system configured to transmit and receive optical energy. The received optical energy may be used to determine object geometric dimensions and/or geometrical proximity to the vehicle 100. It will be noted that radar imaging device 130 is optional and unnecessary to perform many of the methods disclosed herein, wherein processing of visual images is capable of accomplishing clear path detection. The term “clear path” as used herein is to be given its ordinary and customary meaning to a person of ordinary skill in the art (and it is not to be limited to a special or customized meaning), and refers without limitation to a path free of objects exceeding a threshold, e.g., a path free of objects classified in the abovementioned second and third categories.

The processing module 120 is illustrated in FIG. 1, and described herein as a discrete element. Such illustration is for ease of description and it should be recognized that the functions performed by this element may be combined in one or more devices, e.g., implemented in software, hardware, and/or application-specific integrated circuitry. The processing module 120 can be a general-purpose digital computer comprising a microprocessor or central processing unit, storage mediums comprising non-volatile memory including read only memory and electrically programmable read only memory, random access memory, a high speed clock, analog to digital and digital to analog circuitry, and input/output circuitry and devices and appropriate signal conditioning and buffer circuitry. In the alternative, processing module 120 can be a digital signal processing (DSP) unit, such as a customized integrated circuit such as a field programmable gate array. The processing module 120 has a set of processing algorithms, comprising resident program instructions and calibrations stored in the non-volatile memory and executed to provide desired functions. The algorithms are preferably executed during preset loop cycles. Algorithms are executed by the central processing unit and are operable to monitor inputs from the aforementioned sensing devices and execute control and diagnostic routines to control operation of the actuators, using preset calibrations. Loop cycles may be executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, algorithms may be executed in response to occurrence of an event.

The processing module 120 executes algorithmic code stored therein to monitor related equipment such as camera 110 and radar imaging system 130 and execute commands or data transfers as indicated by analysis performed within the processing module. Processing module 120 may include algorithms and mechanisms to actuate autonomous driving control by means known in the art and not described herein, or processing module 120 may simply provide information to a separate autonomous driving system. Processing module 120 is adapted to receive input signals from other systems and the operator as necessary depending upon the exact embodiment utilized in conjunction with the control module.

FIG. 2 illustrates a known method to determine a clear path for autonomous driving in accordance with the present disclosure. Image 10 is generated corresponding to the roadway in front of vehicle 100. Through one of various methods, objects 40A, 40B, and 40C are identified within image 10, and each object is categorized and classified according to filtering and trained object behaviors. Separate treatment of each object can be computationally intensive, and requires expensive and bulky equipment to handle the computational load. An algorithm processes all available information regarding the roadway and objects 40 to estimate a clear path available to vehicle 100. Determination of the clear path depends upon the particular classifications and behaviors of the identified objects 40.

FIG. 3 illustrates an exemplary method to determine a clear path for autonomous or semi-autonomous driving in accordance with the present disclosure. Image 10 is depicted including ground 20, horizon 30, and objects 40. Image 10 is collected by camera 110 and represents the road environment in front of vehicle 100. Ground 20 represents the zone of all available paths open to travel without regard to any potential objects. The method of FIG. 3 that determines a clear path upon ground 20 starts by presuming all of ground 20 is clear, and then utilizes available data to disqualify portions of ground 20 as not clear. In contrast to the method of FIG. 2 which classifies every object 40, the method of FIG. 3 instead analyzes ground 20 and seeks to define a clear path confidence likelihood from available data that some detectable anomaly which may represent object 40 limits or makes not clear that portion of ground 20. This focus upon ground 20 instead of objects 40 avoids the complex computational tasks associated with managing the detection of the objects. Individual classification and tracking of individual objects is unnecessary, as individual objects 40 are simply grouped together as a part of the overall uniform limitation upon ground 20. Ground 20, described above as all paths open to travel without discrimination, minus limits placed on ground 20 by areas found to be not clear, define clear path 50, depicted in FIG. 3 as the area within the dotted lines, or an area with some threshold confidence likelihood of being open for travel of vehicle 100.

Object 40 that creates not clear limitations upon ground 20 can take many forms. For example, an object 40 can represent a discrete object such as a parked car, a pedestrian, or a road obstacle, or object 40 can also represent a less discreet change to surface patterns indicating an edge to a road, such as a road-side curb, a grass line, or water covering the roadway. Object 40 can also include an absence of flat road associated with ground 20, for instance, as might be detected with a large hole in the road. Object 40 can additionally include an indicator without any definable change in height from the road, but with distinct clear path implications for that segment of road, such as a paint pattern on the roadway indicative of a lane marker. The method disclosed herein, by not seeking to identify object 40 but by taking visual cues from ground 20 and anything in proximity to the ground in image 10, evaluates a clear path confidence likelihood of clear versus not clear and adjusts the control of vehicle 100 for the presence of any object 40.

Numerous methods for automated analysis of two-dimensional (2D) images are possible. Analysis of image 10 is performed by an algorithm within processing module 120. FIG. 4 illustrates one exemplary method which may be applied to analyze image 10 in accordance with the present disclosure. This method subdivides image 10 and identifies a sub-image or patch 60 of ground 20 for analysis, extracts features or analyzes the available visual information from patch 60 to identify any interesting or distinguishing features within the patch, and classifies the patch according to a confidence likelihood of being a clear path according to analysis of the features. Patches with greater than a certain threshold of likeliness are classified as clear, and a compilation of patches can be used to assemble a clear path within the image.

Patch 60, as a sub-image of image 10, can be identified through any known means, such as random search or swarm search of image 10. Alternatively, information regarding the presence of an object 40 available from some other source of information, such as radar imaging system 130, can be used to identify a patch to analyze the portion of image 10 which should describe object 40. Image 10 may require many patches 60 to analyze the whole image. In addition, multiple overlaying patches or patches of different size could be used to fully analyze a region of image 10 containing information of interest. For instance, a small patch 60 might be used to analyze a small dot on the road; however, a large patch 60 might be required to analyze a series of dots which in isolation might seem uninteresting, but in context of the entire series, could indicate an object 40 of interest. In addition, the resolution of patches applied to a particular area may be modulated based upon information available, for instance, with more patches being applied to a region of image 10 wherein an object 40 is thought to exist. Many schemes or strategies can be utilized to define patches 60 for analysis, and the disclosure is not intended to be limited to the specific embodiments described herein.

Once a patch 60 has been identified for analysis, processing module 120 processes the patch by applying known feature identification algorithms to the patch. Additionally, processing module 120 may perform analysis of the location of the patch in context to the location of the vehicle. Feature identification algorithms search available visual information for characteristic patterns in the image associated with an object including features defined by line orientation, line location, color, corner characteristics, other visual attributes, and learned attributes. Feature identification algorithms may be applied to sequential images to identify changes corresponding to vehicle motion, wherein changes not associated with ground movement may be identified not clear path. Learned attributes may be learned by machine learning algorithms within the vehicle, but are most frequently programmed offline and may be developed experimentally, empirically, predictively, through modeling or other techniques adequate to accurately train distinguishing attributes.

Once features in patch 60 have been extracted, the patch is classified on the basis of the features to determine the confidence likelihood that the patch is a clear path. Likelihood analysis is a process known in the art by which a likelihood value or a confidence is developed that a particular condition exists. Applied to the present disclosure, classification includes likelihood analysis to determine whether the patch represents a clear path or if ground 20 in this patch is limited by an object 40. Classification is performed in an exemplary embodiment by application of classifiers or algorithms trained with a database of exemplary road conditions and interactions with detected objects. These classifiers allow processing module 120 to develop a fractional clear path likelihood value for patch 60, quantifying a confidence between zero and one that the features identified within the patch do not indicate a limiting object 40 which would inhibit free travel of vehicle 100. A threshold confidence can be set, defining the clear path likelihood required to define the patch as a clear path, for instance by the following logic:

Confidence=ClearPathLikelihood(i)

If_Confidence>0.5, then patch=clearpath  (1)

In this particular exemplary embodiment, a confidence of 50% or 0.5 is selected as the threshold confidence. This number can be developed experimentally, empirically, predictively, through modeling or other techniques adequate to accurately evaluate patches for clear path characteristics.

The likelihood analysis, as mentioned above, may be performed in one exemplary embodiment by application of trained classifiers to features extracted from a patch. One method analyzes the features a-priori using a training set of images. In this training stage, distinguishing features are selected from a raw feature set, the distinguishing features being defined by methods known in the art, such as Haar wavelet, Gabor wavelet, and Leung-and-Malik filter bank. In addition, 2D image location information based on each feature's minimal classification errors, calculated as the sum of false acceptance rate (FAR) and false rejection rate (FRR), may be utilized by tuning a single threshold as illustrated in FIG. 5. This classification error can be described through the following expression:

ClassificationError(i)=FAR_(i)+FRR_(i)  (2)

Information from the trained classifiers is used to classify or weight the feature as indicating a clear path or not clear path, the particular classification depending upon the strength of comparisons to the trained data. Classification of the feature, if the feature is the only feature within the patch, may be directly applied to the patch. Classification of a patch with multiple features identified may take many forms, including the patch being defined by the included feature most indicative of the patch being not clear or the patch being defined by a weighted sum of all of the features included therein.

The above method can be utilized to examine an individual image 10 and estimate a clear path 50 based upon visual information contained within image 10. This method may be repeated at some interval as the vehicle travels down the road to take new information into account and extend the formulated clear path to some range in front of the vehicle's new position. Selection of the interval must update image 10 with enough frequency to accurately supply vehicle 100 with a clear path in which to drive. However, the interval can also be selected to some minimum value to adequately control the vehicle but also not to unduly burden the computational load placed upon processing module 120.

Clear path detection can be accomplished through a single image 10 as described above. However, processing speed and accuracy can be improved with the addition of a second image taken in close time proximity to the original image, such as sequential images from a streaming video clip. A second image allows direct comparison to the first and provides for updated information regarding progression of the vehicle and movement of detected objects. Also, the change of perspective of camera 110 allows for different analysis of features from the first image: a feature that may not have shown up clearly or was indistinct in the first image may display at a different camera angle, stand out more distinctly, or may have moved since the first image, allowing the classification algorithm an additional opportunity to define the feature.

Processing of a second image in relation to the original image 10 can be performed by calculating an image difference. If the image difference of a point of interest, such as a feature identified by radar, is not zero, then the point can be identified as embodying new information. Points where the image difference does equal zero can be eliminated from analysis and computation resources may be conserved. Methods to determine image difference include absolute image intensity difference and vehicle-motion compensated image difference.

Determining an image difference by calculating an absolute image intensity difference can be used to gather information between two images. One method of absolute image intensity difference includes determining equivalent image characteristics between the original image and the second image in order to compensate for movement in the vehicle between the images, overlaying the images, and noting any significant change in intensity between the images. A comparison between the images indicating a change in image intensity in a certain area contains new information. Areas or patches displaying no change in intensity can be de-emphasized in analysis, whereas areas displaying clear changes in intensity can be focused upon, utilizing aforementioned methods to analyze patches on either or both captured images.

FIGS. 6A, 6B, and 6C illustrate an exemplary determination of an image difference by calculating an absolute image intensity difference in accordance with the present disclosure. FIG. 6A depicts an original image. FIG. 6B depicts a second image with changes from the original image. In particular the depicted circular shape has shifted to the left. A comparison of the two images as illustrated in FIG. 6C, an output representing the result of an absolute image intensity difference comparison, identifies one region having gotten darker from the first image to the second image and another region having gotten lighter from the first image to the second image. Such a method can be described as differencing. Analysis of the comparison yields information that some change as a result of movement or change of perspective is likely available in that region of the images. In this way, absolute image intensity difference can be used to analyze a pair of sequential images to identify a potentially not clear path.

Likewise, determining an image difference by calculating a vehicle-motion compensated image difference can be used to gather information between two images. Many methods to calculate a vehicle-motion compensated image difference are known. One exemplary method of vehicle-motion compensated image difference includes analyzing a potential object as both a stationary portion of a clear path and a detected object at the same time. Likelihood analysis is performed on features identified corresponding to the potential object from both classifications at the same time, and the classifications may be compared, for example, through the following logic:

Confidence(i)=ClearPathLikelihood(i)−DetectedObectLikelihood(i)

If_Confidence>0, then patch=clearpath  (3)

In this exemplary comparison, if confidence(i) is greater than zero, then the patch containing the feature is classified as a clear path. If confidence(i) equals or is less than zero, then the patch containing the feature is classified as not a clear path or limited. However, different values may be selected for the confidence level to classify the patch as a clear path. For example, testing may show that false positives are more likely than false negatives, so some factor or offset can be introduced.

FIG. 7 illustrates one method to classify a feature as a portion of a clear path and as a detected object at the same time as described above in accordance with the present disclosure. Image 10 includes object 40, trapezoidal projection 70, and rectangular projection 80. This method utilizes an assumption projecting object 40 as a flat object on the ground within projection 70 to test the classification of the feature as a portion of a clear path. The method also utilized an assumption projecting object 40 as a vertical object within rectangular projection 80 to test the classification of the feature as a detected object. FIG. 8 illustrates comparisons made in data collected between the two images to evaluate the nature of object 40 in accordance with the present disclosure. Camera 110 at time t₁ observes and captures data from object 40 in the form of a first image. If object 40 is an actual detected object, the profile observed by camera 110 of object 40 at time t₁ will correspond to point 90A. If object 40 is a flat object in the same plane as ground 20, then the profile observed by camera 110 of object 40 at time t₁ will correspond to point 90B. Between times t₁ and t₂, camera 110 travels some distance. A second image is captured at time t2, and information regarding object 40 can be tested by applying an algorithm looking at visible attributes of the object in the second image in comparison to the first image. If object 40 is an actual detected object, extending upward from ground 20, then the profile of object 40 at time t₂ will be observed at point 90C. If object 40 is a flat object in the same plane as ground 20, then the profile of object 40 at time t2 will be observed at point 90B. The comparison derived through vehicle-motion compensated image difference can directly assign a confidence by application of classifiers based on the observations of points 90, or the comparison may simply point to the area displaying change as a point of interest. Testing of the object against both classifications, as a flat object and as an actual detected object, allows either the area including object 40 to be identified for further analysis through analysis of a patch as described above or direct development of a clear path likelihood and a detected object likelihood for comparison, for example as in logic expression (3) above.

Information available from analysis of the second image can additionally be improved by integration of information regarding movement of the vehicle, such as speed and yaw-rate. Information regarding vehicle motion is available from a number of sources, including the vehicle speedometer, vehicle dynamic sensors or wheel speed sensors, anti-lock braking mechanisms, and GPS location systems. Algorithms may utilize this vehicle movement information, for example, in conjunction with the projections described in FIGS. 7 and 8 to project angles which should exist in a feature laying flat on the ground in the second image based upon data from the first image and the measured movement of the vehicle between the images.

The number of images utilized for comparison need not be limited to two. Multiple image analysis can be performed at multiple iterations, with an object being tracked and compared over a number of cycles. As mentioned above, computational efficiency can be gained by utilizing image difference analysis to identify points of interest and eliminating areas with zero difference from subsequent analyses. Such efficiencies can be used in multiple iterations, for example, saying that only points of interest identified between a first and second image will be analyzed in the third and fourth images taken. At some point, a fresh set of images will need to be compared to ensure that none of the areas showing zero difference have had any change, for example a moving object impinging upon a previously identified clear path. The utilization of image difference analyses and of focused analyses, eliminating areas identified with zero change, will vary from application to application and may vary between different operating conditions, such as vehicle speed or perceived operating environment. The particular utilization of image difference analyses and of focused analyses can take many different embodiments, and the disclosure is not intended to be limited to the specific embodiments described herein.

Multiple methods are herein disclosed for using the clear path detection analysis to identify a clear path including patch-based methods, pixel-based methods, and an example-based method. The methods herein are preferably executed in the processing module 120, but may be combined in one or more devices, e.g., implemented in software, hardware, and/or application-specific integrated circuitry. Patch-based methods are described above and herein with reference to FIG. 9. Pixel-based methods are described herein with reference to FIGS. 11 and 12. It will be appreciated that pixel-based methods make decisions based upon pixel or a group of pixels. This decision for the component patch being analyzed can be based upon pixels contained within the patch, for example, with the patch being determined to be unclear if any or some minimum number of pixels within the patch are determined to be not clear. Exemplary pixel-based methods include textureless and texture-rich methods. Texture-rich methods analyze pixelated features in an image for distinct interest points based upon a contextual view within the image. The interest points are mapped corresponding to a field-of-view in from on the vehicle 100 and a clear path is determined based upon topography of the interest points within the map. Textureless methods filter from an image non-conforming regions of the image as not belonging to a planar, consistent road surface, remaining pixels correspond to the clear path. Patch-based methods are computationally, relatively fast, pixel-based methods can be computationally, relatively slow while example-based methods are computationally slower, by comparison.

FIG. 9 illustrates an exemplary patch-based method 200 wherein input from a camera is analyzed to determine a clear path likelihood in accordance with the present disclosure. The patch-based method 200 is illustrated in FIG. 9, and described herein as comprising discrete elements. Such illustration is for ease of description and it should be recognized that the functions performed by these elements may be combined in one or more devices, e.g., implemented in software, hardware, and/or application-specific integrated circuitry. For example, the patch-based method 200 may be executed as one or more algorithms in the processing module 120.

During operation, the camera 110 generates an image for analysis in the processing module 120 (202). The processing module 120 identifies patches in the image and selects a patch for analysis (204). Multiple methods for defining a plurality of patches sufficient to adequately analyze the image are contemplated by this disclosure. As described above, patches may be defined according to random search or swarm search methods. Alternatively, information from some other source of information, such as a radar imaging system, can be used to define a patch to analyze the portion of the image. In addition, multiple overlaying patches can be utilized based upon the perceived area of interest upon the image to be analyzed. Additionally, methods can be utilized to define patches according to anticipated road surface in front of the vehicle and resulting clear path patterns, for example, including a fixed-grid patch method, sectioning off some or all of the image according to a regular patch pattern, and a perspective patch method, similar to the fixed-grid patch method except that the patch sizes and/or shapes are modulated based upon a perspective view of the road and consideration for an amount of road surface contained within each of the patches. Such an anticipated road surface in front of the vehicle can be adjudged by an initial review of the input image, for example, utilizing clearly visible lines that could define lane boundaries as an initial reference to define a patch pattern. In another example, a patch pattern from an immediately previous iteration of the clear path method could be utilized and slowly modulated through the iterations, based upon the iteratively defined clear path and other indications that can be identified within the analyzed images.

The fixed-grid patch method identifies and divides the image into a plurality of patches based upon an area of interest and applies a fixed-grid pattern to the area of interest. The fixed-grid pattern sections substantially the entire area of interest in patches. The area of interest preferably encompasses the field-of-view immediately in front of the vehicle, however the area may be defined to encompasses more narrow fields-of-view. In one embodiment, the area of interest encompasses the field-of-view immediately in front of the vehicle and delimited by a horizon line or a vanishing point perceived for the roadway. The fixed-grid patch method can include patch tracking, identification, and analysis via a matrix, wherein each patch may be identified by a number of a number series.

The fixed-grid patch may be applied to the image using a number of methods. A first method includes applying the fixed-grid patch to sequential images using equal image coordinates. A second method includes applying the fixed-grid patch to the image using an identified interest point on the image, e.g., the horizon line. A third method includes applying the fixed-grid patch to the image compensating for vehicle movement, e.g., vehicle yaw.

The perspective patch method identifies and divides the image into a plurality of patches based upon field-of-view coordinates rather than image coordinates. An area of interest is identified as described hereinabove, wherein a perspective patch pattern is applied to the area of interest based upon estimated field-of-view coordinates, allocating patch size relative to an approximate area of ground covered by each patch. Such perspective patch definitions allow for a more detailed review of patches describing ground closer to the vehicle and less wasteful review of patches describing ground more distant from the vehicle. Patches can be aligned to the perceived lanes of travel upon the roadway, for example, as defined by lane markers and/or curbsides. Such patch definitions will frequently be trapezoidal, with the parallel sides of the trapezoids being parallel to the horizon or horizontal axis of the vehicle, and with the remaining sides of the trapezoids being dependent upon the define road surface in the image view. Such a patch alignment is efficient to defining the road surface. However, computation of the grid of patches and the analysis of the patches is complicated by the many different shapes. The patches can instead be normalized to rectangle (or square) shapes, still parallel to the horizon or horizontal axis of the vehicle. Such rectangular patches are in ways less efficient in covering the road surface, for example, with portions of the curbside overlapping patches including actually clear roadway, but sufficient resolution of the patches and improved the computational efficiency can make such normalized perspective patches beneficial.

A filter or a set of filters may be applied to the selected patch (206), e.g., a lighting normalization filter. An exemplary normalization filter changes the range of pixel intensity values within the patch, thereby bringing the patch into a range that is more suitable for machine processes. For example, normalizing each pixel value to a zero mean and unit variance enhances the image contrast, specifically in a low lighting environments or when contrast is poor due to glare. A number of exemplary filters and filtering methods useful for image analysis are envisioned, and the disclosure is not intended to be limited to the particular exemplary embodiments described herein.

After filtering, feature extraction is executed on the selected patch using feature extraction algorithms (208). Feature extraction algorithms may analyze the selected patch for predetermined features, e.g., edges, corners, and blobs, and/or shapes, e.g., circles, ellipses, and lines. It will be appreciated that some features have meaning and others do not, and a process of feature selection can be utilized to identify a group of best features for analysis. A classifier training algorithm analyzes each feature and assigns a likelihood value (210). As mentioned above, classifiers or logic used in developing likelihood values are initially trained offline. Training may optionally be continued in the vehicle based upon fuzzy logic, neural networks, or other learning mechanisms known in the art. These trained classifiers perform a likelihood analysis upon the features extracted, and a likelihood value for the patch determined. This likelihood value expresses a confidence that the selected patch is clear.

The likelihood analysis may be augmented using spatially and/or temporally related patches to evaluate identified features during vehicle operation. When the feature extraction algorithm has identified a feature, the processing module 120 may spatially analyze the identified feature for consistency among adjacent or nearby patches. A feature identified in one patch may be compared to surrounding patches to determine if it is an aberration or consistent with the surrounding patches. A feature that is consistent with surrounding patches may be assigned a similar likelihood value to the surrounding patches, whereas a feature not consistent with surrounding patches can be assigned a different likelihood value. Similarly to the spatial analysis, when the feature extraction algorithm has identified a feature, the processing module 120 may temporally analyze the identified feature for consistency among temporally related patches, compensating for vehicle motion. For example, a feature analyzed in several frames and determined to have a high likelihood value through the image frames can be temporally compared to the same feature receiving a low likelihood value in a later frame. If the temporal analysis of the feature reveals new information, such as movement of the feature with respect to the roadway or increased perspective revealing the feature to be indicative of an object situated upon the road surface, then the lower likelihood value for the feature can be confirmed. If no new information is available, then the lower likelihood value for the feature in the present frame can be suspended as not necessarily indicating a not clear path. Subsequent frames can be analyzed similarly to establish the feature as significant or not. Similarly, according to methods described herein, the questionable feature can be analyzed with increased computational emphasis, either in the present image or in subsequent images.

The processing module 120 compares the likelihood value to a threshold likelihood value (214). If the likelihood value is greater than the threshold value, then the patch is identified as a clear path (218). If the likelihood value is not greater than the threshold value, then the patch is identified as a not clear path.

As described above, the patch-based method 200 may be repeated or reiterated in a number of ways, with the same image being analyzed repeatedly with the selection and analysis of different patches, and an identified patch can be tracked and analyzed for change over a number of sequential images.

FIG. 10 illustrates an exemplary texture-rich pixel-based method 300 wherein input from a camera is analyzed to determine a clear path likelihood in accordance with the present disclosure. The texture-rich pixel-based method 300 is illustrated in FIG. 10, and described herein as comprising discrete elements. Such illustration is for ease of description and it should be recognized that the functions performed by these elements may be combined in one or more devices, e.g., implemented in software, hardware, and/or application-specific integrated circuitry. For example, the pixel-based method 300 may be executed as one or more algorithms in the processing module 120.

During operation, the camera 110 generates an image for analysis in the processing module 120 (302). The processing module 120 analyzes the image for interest points, for example, examining pixel color intensity as described hereinabove and comparing the pixel or a group of pixels with surrounding pixels. An interest point is an identifiable pixel on an image and is associated with a set of visual information, i.e., texture-rich features, and is associated with objects located in the field-of-view. Through methods known in the art, e.g., a scale-invariant feature transform (SIFT), methods employing corner detection or other shape detection, or a Sobel filter, interest points can be identified and utilized to accomplish methods described herein (306). In one embodiment, redundant interest points, e.g., multiple interest points corresponding to the same feature, are removed for computational efficiency considerations.

Once the interest points are identified, the processing module 120 compares sequential images when the vehicle is in motion to match interest points from each image to corresponding points in the sequential images which correspond to the same points in the field-of-view, where possible (310). Matching includes using correspondence matching programming, e.g., a scale-invariant feature transform (SIFT) feature matching programming and optical flow programming, and may further include locating corresponding points through template matching, taking into account movement of the host vehicle, and making a best estimate whether two points represent the same object or feature visible in the field-of-view. Template matching may be determined using one of multiple methods, including one of several known template matching programming methods to find the corresponding interest points, e.g., Lucas-Kanade or Horn-Schunck. The resulting matched point pairs correspond to a same feature located on both images wherein the same feature is associated with a same object in the field-of-view. While interest points can be matched, not all matched corresponding point pairs represent high quality corresponding point pairs that allow the identification of their three-dimensional positions in the field-of-view for classifications as a clear path for the vehicle to travel through.

The processing module 120 filters the matched corresponding point pairs in order to identify high quality corresponding point pairs that can be utilized for three-dimensional position identification with high confidence (314). Preferential matched point pairs may be selected based upon quality control criteria, e.g., distance between points, distance from image boundary, and color similarities between respective neighboring pixels. Selection of criteria to judge matched pairs can additionally be made based upon conditions such as light level present outside the vehicle, weather, speed of the vehicle, and any other factor affecting an ability to judge matched pairs or an urgency to quickly and accurately define a clear path.

The high quality corresponding point pairs are analyzed to determine three-dimensional positions of objects in the field-of-view represented by the corresponding point pairs (318). It will be appreciated that corresponding points at different heights as compared to ground level will move differently between sequential images. Analyzing movement of the interest points between sequential images can yield estimated three-dimensional coordinates of the interest points. Object position can be determined based upon the high quality corresponding point pairs, sample time between sequential images, and vehicular data such as vehicle speed, and vehicle yaw rate. These methods of triangulation can yield a position of the object in a horizontal plane and a height of the object in relation to a ground level.

The determined object positions are utilized to map object positions in front of the host vehicle including an estimated topography of the field-of-view (322). The topography may be estimated by assigning predetermined spatial dimensions around the object. Preferably, the predetermined spatial dimensions diminish with respect to height at a predetermined rate with respect to distance from the object. Using the map and estimated topography the processing module 120 can determine a clear path in front of the host vehicle (326).

The above method utilizes sequential images to establish a map of object positions and vertical heights in front of the vehicle, such that a clear path can be defined. It will be appreciated that in any two given images, a particular object might not be classified as including two high quality interest points sufficient to be mapped in that particular analysis. However, the above analysis occurs multiple times per second of vehicle travel. As the vehicle travels forward through the clear path, different perspectives upon an object will be gained and a large number of images will be analyzed. Travel over a path and analysis of the multiple iterative images through that path build a confidence through the analyses that no object contradicting the clear path exists in the identified clear path.

FIG. 11 illustrates an exemplary textureless pixel-based method 400 wherein input from a camera is analyzed to determine a clear path likelihood in accordance with the present disclosure. The textureless pixel-based method 400 is illustrated in FIG. 11, and described herein as comprising discrete elements. Such illustration is for ease of description and it should be recognized that the functions performed by these elements may be combined in one or more devices, e.g., implemented in software, hardware, and/or application-specific integrated circuitry. For example, the textureless pixel-based method 400 may be executed as one or more algorithms in the processing module 120.

During operation, the camera 110 generates an image for analysis in the processing module 120 (453). The processing module 120 analyzes the image using multiple filtering methods to identify and remove non-conforming pixels from the image. Remaining pixels indicate a potential clear path for the vehicle to travel. FIG. 11 shows the textureless pixel-based method 400 including four exemplary filtering methods to identify and remove non-conforming pixels from the image. A textureless method could be used with some portion of the four exemplary methods and/or can include unnamed but similar methods to process the image.

A first exemplary filtering method removes pixels above a horizon or vanishing point, including sky and other vertical features that cannot be part of a road surface (456). The term “vanishing point” as used herein is a broad term, and is to be given its ordinary and customary meaning to one ordinarily skilled in the art, and refers to an infinite far point on the horizon that is intersected by multiple parallel lines on the ground in the view. Identifying a road surface creating a clear path on which to drive is necessarily below the vanishing point or horizon line. Filtering images to only analyze an area below the horizon line helps to clarify the pixels being analyzed to identify a road surface from irrelevant pixels. As one skilled in the art appreciates, there are many known methods for determining a vanishing point and corresponding horizon line.

A second exemplary filtering method applies a filter based upon variance in pixel color intensity, based upon a premise that a road surface will include a large surface with a visual intensity common across the surface (459). Pixels are removed from the image when an associated pixel color intensity varies greater than a predetermined threshold. For pixels associated with multiple colors, a pixel color intensity of any particular color that varies greater than the predetermined threshold may be removed from the image. The predetermined threshold may be updated based upon historical color intensity of pixels identified as clear.

A third exemplary filtering method applies a filter based upon differencing sequential images, allowing analysis of changes between the images (462). Pixels associated with a pixel color intensity that changes greater than a predetermined threshold from the sequential images may be removed from the image. In one embodiment, the adjustments are made to the images based upon motion of the vehicle so that pixels are differenced and compared as if all pixels correspond to points at a ground level. Known triangulation methods may be used for determining motion adjustments to the images. By using an assumption that all objects in the image are at ground level, non ground level points may be identified by changes not consistent with pixels associated with the ground level. For example, pixels above ground level may move faster between sequential images than would be expected, and this movement may be identified by examining the difference between pixel color intensities between sequential images.

A fourth exemplary filtering method applies a filter based upon identifying pixels representing edges or transitions in the visual data (465). To create the fourth filtered image, the processing module 120 extracts pixels from the image based upon color intensity values that correspond to edges using one of several known edge detection filters, e.g., a Sobel filter. The edge detection filter is preferably executed in the processing module 120, but may be combined in one or more devices, e.g., implemented in software, hardware, and/or application-specific integrated circuitry. In one embodiment, each pixel is analyzed using a Sobel operator. The Sobel operator computes a gradient vector of color intensity at each pixel resulting in a direction of the largest possible increase from light to dark and the rate of change in that direction. Points corresponding to a rate of change exceeding a threshold and corresponding to gradient vectors at nearby pixels indicate edges and are included in the fourth filtered image. Those pixels are included in the image while the others are removed.

Applying the various methods in parallel, the results can be the fused into a single map of the image (468). Fusion includes pixels identified in each of the various filtering methods. Pixels on the fused clear path map correspond to desirable driving locations in the field-of-view. Locations on the fused clear path map without pixels correspond to undesirable driving locations in the field-of-view. The processing module 120 may analyze the map for visual data indicative of a clear path of travel (471).

The textureless pixel-based method 400, described in FIG. 11, applies various methods to images in parallel to identify features in a view relevant to defining a clear path. However, it will be appreciated that these methods need not be performed in parallel, but rather the methods can be used to process images sequentially in steps or selectively to identify features in a view relevant to defining a clear path.

An addition pixel-based clear path detection method includes applying a fused texture-rich and textureless method.

The texture-rich and textureless methods can be fused in a number of ways. An image with identified points and determined heights identified with texture-rich methods can be overlaid with a filtered image generated by textureless methods, and agreement of the two methods can be used to define a clear path through the overlaid image. In an alternative method to fuse the two schemes, the data from each of the two schemes can be used to project information upon a programmed overhead map of an area in front of the vehicle, and this overhead map including data gained from analysis of the two schemes can include building confidence indications for regions of the map. In an alternative method to fuse the two schemes, one scheme can be utilized as a primary or dominant scheme, and the second scheme can be utilized or activated to analyze regions in the view identified as ambiguous or unclear. In any method to fuse the two schemes, strengths of one processing scheme can be used to reduce weaknesses of the other processing scheme. If both schemes concur that the path is clear, then the processing module employing the schemes may determine with increased confidence that the path is desirable for the vehicle to traverse. A number of methods to fuse the identified schemes are envisioned, and the disclosure is not intended to be limited to the particular embodiments described herein. Additionally, either scheme or both schemes can be combined with the method employed above utilizing analysis of patches.

As described above, an example-based method can be utilized alternatively or additionally to define a clear path based upon an input image. An exemplary example-based method collects a number of sample images of views, defining a clear path for each of the sample images, matches a current image to one or more of the sample images, and determines a clear path based upon the matching. Matching the current image to one or more of the sample images can be accomplished, for example, by extracting features from each of the sample images, extracting features from the current image, comparing the extracted features from the current image to a database of extracted features from the sample images, and selecting matching sample images to the current image. A clear path can be selected from the best matching sample image or can be determined based upon a combination of the closest matches to the current image.

An additional method is disclosed for detecting a clear path of travel for a vehicle by segmenting an image generated by a camera device located upon the vehicle. This segmentation-based method includes monitoring the image, analyzing the image to segment a region of the image that cannot represent the clear path of travel from a region of the image that can represent the clear path of travel, defining the clear path of travel based upon the analyzing, and utilizing the clear path of travel to navigate the vehicle. Analysis methods used to segment the image include but are not limited to a motion analysis between a plurality of sequential images to identify a region of the image that cannot be the clear path, a texture analysis of the image to identify a region of the image that cannot be the clear path, a color analysis of the image to identify a region of the image that cannot be the clear path; and a geometric analysis of the image to identify a region of the image that cannot be the clear path.

Hierarchical configurations of multiple clear path detection algorithms may be incorporated into this disclosure, including algorithms arranged based upon computational intensity. Less computationally intensive detection methods can identify clear paths in the image and leave remaining sections of the image not identified as a clear path for more computationally intensive analysis thereby increasing computational efficiency for clear path identification. The particular methods utilized and the hierarchical structure of the particular hierarchical method used can differ or change. In an exemplary hierarchical configuration, a patch-based clear path detection method identifies clear paths in the image before a pixel-based clear path detection method analyzes the remaining sections of the image not identified as a clear path by the patch-based method. In one embodiment, a second exemplary hierarchical layer utilizing an example-based method further analyzes sections not identified as a clear path by the pixel-based method. However, a number of different hierarchical configurations are envisioned, and the disclosure is not intended to be limited to the particular embodiments described herein.

One skilled in the art will recognize that lighting normalization may be applied to the captured image data. Normalization is a process which changes the range of pixel intensity values. The purpose of the normalization is to bring the image into a range that is more suitable for machine process to improve the reliability. For example, each pixel value is normalized to be a zero mean and unit variance to enhance the image contrast, specifically in a low lighting environment or when contrast is poor due to glare.

Additional methods are herein disclosed for detecting a clear path of travel for the vehicle 100 including methods based upon topographical variation in a region of a roadway in front of the vehicle. Two exemplary methods to estimate topographical variation in front of the vehicle include ground plane estimation analysis and snow elevation change detection analysis. Clear path detection methods described above, including patch-based, pixel-based, and example-based methods, may be augmented using the ground plane estimation analysis and snow elevation change detection analysis. Ground plane estimation analysis and snow elevation change analysis estimate surface topography to determine clear paths for the vehicle 100. Both methods for analyzing a roadway can be used to strengthen confidence in clear paths identified in the field-of-view. Similarly, clear path detection analysis can be used to augment the ground plane estimation analysis and the snow elevation change analysis as described herein below.

Ground plane estimation analysis, or compiling a map describing height variation in the surface in front of the vehicle, is useful to describe a flat surface upon which the vehicle may be driven. It will be appreciated that flat does not preclude driving upon a hill or curved road surface, but rather points to an acceptably uniform surface allowing regular travel of the vehicle. In one embodiment, the estimated ground plane corresponds to image coordinates associated with an estimated ground level. Ground plane estimation analysis may be camera-based or light detection and ranging-based (LIDAR-based). In one exemplary embodiment, camera-based ground plane estimation analysis includes tracking features or identifiable points between two or more images and determining a height of the feature based upon movement of the feature relative to the camera. In another exemplary embodiment, LIDAR-based ground plane estimation includes emission of optical energy and analysis of the returning signal to estimate a ground plane in front of the vehicle.

Snow elevation change analysis is similarly useful to describe a flat surface upon which the vehicle can be driven. When LIDAR is available upon a vehicle, then the height and changes in height in snow can be directly measured. However, it will be appreciated that snow covered roads or driving environments can be difficult to analyze by typical camera detection methods. Feature tracking from one image frame to the next can be complicated by the lack of contrast in snowy surfaces or the transient and noisy images that can be collected of a snow covered road. However, a method to accurately estimate a significant change or transition in height of the snow in front of the vehicle can be used to identify a road surface for travel.

Other exemplary embodiments are envisioned. For example, one vehicle may incorporate vehicle-to-vehicle communication capabilities to refine and augment ground plane estimation based upon data from other vehicles in traveling in front of the vehicle, the data including but not limited to ground plane estimations in the other vehicles, suspension data in the other vehicles, accelerometer data in the other vehicles, and position data in the other vehicles. Similarly, a vehicle utilizing global positioning data and a digital map database can track ground plane data for a roadway proximate to the vehicle. A number of methods to estimate or determine topographical variation in a region of a roadway in front of the vehicle are envisioned, and the disclosure is not intended to be limited to the particular embodiments described herein.

Camera-based ground plane estimation analysis is herein described with reference to FIGS. 12 and 13. The analysis is executed on sequential images during vehicle operation.

FIG. 12 shows the vehicle 100 with respect to ground 20 during vehicle travel including different camera perspectives of identified features. As FIG. 12 shows, the vehicle 100 travels from a first location to a second location a distance |t₁| from each other. The center of the camera 110 at the first location is identified as point O₁ and the center of the camera 110 at the second location is identified as point O₂. Also illustrated are exemplary feature points P and Q and projection positions p₁ and p₂ of the feature point P in a normalized image plane of the camera 110 identified by line 36.

The processing module 120 determines the ground plane 41 in geographical coordinates based points on the ground and the camera translation direction t₁. Exemplary feature points P and Q are identified on the image using known feature identification algorithms as described hereinabove. Corresponding feature points P and Q in sequential images can be identified using known optical flow estimation algorithms, e.g., a pyramid Lucas-Kanade optical flow estimation algorithm. As one skilled in the art will recognize, vehicle translation direction t₁ may be determined based upon vehicle motion between sequential images. Once the camera translation direction t₁ is determined, a ground plane can be determined based upon feature points, e.g., exemplary points P and Q, and the vehicle translation direction t₁.

FIG. 13 graphically illustrates the camera 110 at locations O₁ and O₂ relative to a ground plane 41. The ground plane 41 is a geometrical region in the image corresponding to the ground 32 in the field-of-view and is defined by geographical coordinates. The ground plane 41 is determined based upon features identified in the image corresponding to the ground 32. The processing module 120 analyzes features identified in the image for ground level correspondence in the field-of-view, based upon the translation direction t₁ and the three-dimensional location of each feature point P determined based upon the corresponding projection positions, using known triangulation methods. Feature points identified as corresponding to the ground level are included in the ground plane 41. The ground plane 41 is estimated based upon the corresponding feature points associated with the ground 32. As one skilled in the art will recognize, features identified in the image corresponding to the ground 32 shape and define the ground plane 41. The ground plane estimation analysis may be repeated or reiterated in a number of ways, with the same image area being analyzed repeatedly with the selection and analysis of different image areas, and an identified feature tracked and analyzed for change over a number of sequential images. LIDAR-based ground plane estimation analysis is herein described for use in ground plane estimation in front of the vehicle. The analysis is preferably executed on sequential images during vehicle operation. Use of LIDAR for such detection is disclosed in co-pending and commonly assigned U.S. patent application Ser. No. 12/175,634, entitled LIDAR BASED GEOMETRIC ROAD CURVE DETECTION, and is incorporated herein by reference. As described hereinabove, the LIDAR-based system transmits and receives optical energy to determine object geometric dimensions and/or geometrical proximity to the vehicle 100. Patterns in the light waves reflecting off these vehicles can be analyzed and ground locations can be estimated. Patterns corresponding to the ground may be developed experimentally or by any method sufficient to estimate patterns for vehicles. A magnitude of the optical energy return describes reflectivity of the surface detected. For example, a road surface and reflective paint utilized in road markers generate distinct differences in the returned light and can be utilized to detect patterns indicating the location of the lane markers. Additionally, the returns can describe a distance to the detected surface. Such a distance across a surface can describe a 3D world coordinates of point detected by the LIDAR. Such 3D coordinates can be used to measure an elevation contour of a ground surface or ground plane in front of the vehicle. As described herein, such a ground plane estimation can be used to map a route of safe travel in front of the vehicle and can similarly be used to create an enhanced clear path of travel. Additionally, LIDAR returns can estimate a texture of the surface, and texture differences detected between the roadway and the median, shoulder, or grass covered side of the road can be used to detect road-edge. Use of LIDAR returns can take many embodiments, and the disclosure is not intended to be limited to the particular exemplary embodiments described herein.

Snow elevation change analysis can be utilized to estimate a road surface or flat area upon which a vehicle can travel. One exemplary method includes utilizing image recognition to estimate locations of tire tracks or grooves pushed into the snow covered surface by traffic ahead of the vehicle. Another exemplary method includes analyzing pixel color and/or intensity changes in the image to determine correspondence with predefined snow elevation categories. Analysis according to pixel changes in an image can be based upon observations in snow appearance in a typical driving environment. For example, undisturbed snow tends to include a surface with little or no variation in pixel color or intensity. Snow upon a lane of travel, particularly upon a lane of travel which has been plowed, treated by a substance to melt the snow, or snow compressed by repeated passing vehicles, tends to exhibit moderate changes in pixel color and intensity. Snow between a lane of travel and an area of undisturbed area, wherein the snow has been displaced to the side of the lane, tends to exhibit large changes in pixel color and intensity. Snow elevation change analysis can be conclusive or inconclusive depending upon analysis of the images. For example, a vehicle travelling over a road that has not yet been traveled upon or plowed will not exhibit the pixel changes described. A vehicle travelling over a road where the snow is not fresh and particulate matter has been dredged up not only upon the road surface but also upon snow surfaces surrounding the roadway will not exhibit the pixel changes described. However, an acceptable pattern, illustrating different pixel change patterns can be utilized as described to define a clear path. An exemplary acceptable pattern can include areas of the image exhibiting large pixel change lining either side of an area of the image exhibiting moderate pixel change. In this way, a significant change in snow height can be estimated based upon recognizable textures in the snow appearance as available by images from a camera.

Snow elevation change analysis may incorporate vehicle-to-vehicle communication capabilities to refine and augment snow elevation change detection analysis. Vehicle-to-vehicle communications can enable refinement of shared snow elevation change detection between vehicles and allow inclusion of a different perspective of the road surface from which to analyze. Vehicles traveling ahead of a trailing vehicle may confirm a snow elevation change for the trailing vehicle. Trailing vehicle will benefit from additional computational cycles of analysis of the roadway supplied by vehicles traveling ahead.

Snow elevation change analysis is herein described with reference to FIGS. 15A and 15B. The analysis is preferably executed on sequential images during vehicle operation.

FIGS. 15A and 15B show an exemplary field-of-view showing exemplary roadway conditions after a snowfall, including exemplary image 600 depicting areas 602, 604, and 606 analyzed using the snow elevation change detection analysis. Image areas within the image include a plurality of spatially related pixels selected for analysis and identifiable by image coordinates. The image areas can be defined using one of multiple methods, including defining the image areas by a group of pixels or using component patches as used in the clear path detection analysis. Snow elevation change analysis is based upon expected roadway conditions after a snowfall that corresponds to the snow elevation categories described hereinabove. Snow generally falls in a consistent distribution throughout the landscape, resulting in a relatively low color intensity distribution variance in image areas corresponding to undisturbed snow. A first exemplary image area 602 in the exemplary image 600 depicts an area having a relatively low color intensity distribution variance. As vehicles traverse the roadways and/or plows remove snow and other debris, snow may become differently distributed in different areas in a field-of-view, resulting in a relatively moderate color intensity distribution variance in image areas corresponding to a clear path and relatively high color intensity distribution variance in image areas corresponding to snow elevation changes. A second image area 606 in the exemplary image 600 depicts this relatively moderate color intensity distribution variance. A third image area 604 in the exemplary image 600 depicts an area corresponding to a significant transitional area, an area of snow elevation change, or a likely boundary to a flat area or lane of travel. Such snow elevation changes can indicate boundaries between clear paths and not clear paths as indicated by previous usage of the road and the impacts upon the appearance of the road.

Exemplary performance of the above snow elevation change analysis is disclosed. During vehicle operation, the processing module 120 identifies image areas in the image for analysis. The processing module 120 determines a color intensity distribution variance of selected image areas using frequency analysis of a plurality of pixels contained in the image areas. As described above, the analysis can include identification of a snow covered road exhibiting an acceptable pattern likely to accurately indicate a clear path. Pixel change distribution variance can be approximated using a frequency of a predetermined pixel change represented in the image areas. Image areas corresponding to a low frequency of the predetermined pixel change, i.e., less than a first predetermined pixel change threshold, indicate a not clear path. Images areas corresponding to high frequency of the predetermined pixel change, i.e., greater than a second predetermined pixel change threshold, indicate a snow elevation change and may include a border between image coordinates associated with a clear path and not clear path or vehicle tracks in a clear path. Image areas corresponding to a moderate frequency of the predetermined pixel change, i.e., between the first and second predetermined pixel change thresholds indicate a clear path.

As described above, the different thresholds and frequencies involved are useful to approximate a location of a significant change in height. However, it will be appreciated that an isolated pile of disturbed snow exhibiting an appearance falling within the required thresholds by itself does not indicate an acceptable pattern likely to accurately indicate a clear path. Instead, such a visible pattern in a group of areas analyzed must together describe a clear path which the vehicle can travel through. For example, a requirement to define the clear path can include that a pattern of image areas 604 must form a line to infer a boundary of a lane of travel. Another exemplary requirement can include that the detected line must be parallel to other detected lines to form a distinct roadway upon which a clear path can be estimated. It will be appreciated that snow piles are not necessarily uniform, and that determination that a line or lines of image areas 604 must include a threshold tolerance of deviation from an ideal line to still create an acceptable pattern describing an orientation for the proposed boundary to the roadway.

Alternatively, image areas corresponding to a predetermined range of the predetermined pixel change indicate a clear path. The precise pixel change of the predetermined pixel change may be developed experimentally or by any method sufficient to estimate or evaluate the pixel change distribution variance of an image area. The precise pixel change thresholds may be developed experimentally or by any method sufficient to estimate the pixel change distribution variance that indicates one of the snow elevation categories. In one exemplary embodiment, pixel change thresholds can be set dynamically. Because light levels and other factors can significantly change the appearance of pixels in a particular image, a method to scan through different threshold values for a given image can be useful to calibrate to find useful information. Such an exemplary system can make multiple analyses of a single image and utilize pattern recognition to determine a set of threshold values that best identify useful information regarding the road surface. In this way, changes in pixel color or intensity can be utilized to estimate a clear path upon a snowy surface.

As described above, changes in pixels in an image can be utilized to describe significant changes in snow elevation indicative of a clear path or not clear path. Such analysis can be done in localized areas, for example, utilizing patches to classify different areas of the image. As described above, a requirement that the localized areas together reveal an orientation in the estimated boundaries can be defined. Such an analysis of the overall image can be augmented, for example, by comparison to a digital map and a location based upon global positioning. Such a method can overlay features such as vehicle tracks or detected snow elevation transitions to known road geometry in order to improve confidence in the detected clear path. As described herein above, the clear path detection analysis by methods such as patch-based, pixel-based, segmentation-based or example-based methods may be augmented with ground plane estimation analysis and snow elevation change detection analysis methods. Multiple methods for augmenting the clear path detection analysis are contemplated by the disclosure, including augmenting the clear path detection analysis with both the estimated ground plane and the snow elevation change detection analysis. A likelihood analysis may be adopted to incorporate confidence values assigned for both the estimated ground plane and features identified using the snow elevation change detection analysis. However, the order of the methods used or disqualification or substitution of one of the methods can be implemented based upon perceived factors, e.g., detected snow in the roadway. Similarly, an urban environment with rapidly changing traffic conditions or pedestrian traffic may yield particularly poor results for one of the methods. Contamination of the image from the camera caused by a spot upon the lens of the camera may similarly cause poor results from one of the methods. Vehicle speed may affect the quality of results from one of the methods. Such factors can be determined experimentally, computationally, or be judged based upon modeling or any other method sufficient to accurately estimate effectiveness of the various clear path methods to determine a clear path based upon the input image. Additionally, methods such as machine learning algorithms or fuzzy logic can be implemented to adapt selection of the methods based upon in-vehicle use of the various clear path methods and the resulting operation of the vehicle. Such operation of the vehicle can be judged in many ways known in the art, such as monitoring an occurrence of operator intervention in control of the vehicle or by monitoring location of lane markers in images describing subsequent control of the vehicle upon the roadway. A number of methods to select among the methods and to adjust selection of the various clear path methods are envisioned, and the disclosure is not intended to be limited to particular exemplary embodiments disclosed herein.

FIG. 16 illustrates an exemplary method 800 for augmenting the clear path detection analysis with the topographical variation analysis in accordance with the present disclosure. The method 800 is illustrated in FIG. 16, and described herein as comprising discrete elements. Such illustration is for ease of description and it should be recognized that the functions performed by these elements may be combined in one or more devices, e.g., implemented in software, hardware, and/or application-specific integrated circuitry. For example, the method 800 may be executed as one or more algorithms in the processing module 120.

During operation, the camera 110 generates an image for analysis in the processing module 120 (802). The processing module 120 applies a parallel processing approach that includes concurrently analyzing the image using the clear path detection analysis and one of the exemplary snow elevation change detection analysis or ground plane detection analysis methods disclosed herein. In the exemplary embodiment depicted, ground plane estimation analysis generates the ground plane estimate (804). It will be appreciated that a similar embodiment could have utilized a LIDAR method including a LIDAR device input in the place of the depicted structure of step 804. An exemplary clear path detection analysis, for example, utilizing a fusion of texture-rich and textureless methods, identifies image areas corresponding to a clear path (806). The outputs of steps 804 and 806 are compared and utilized to form an enhanced clear path in step 808.

The estimated ground plane is used in the clear path detection analysis to enhance or refine image areas corresponding to a clear path. The estimated ground plane can be used in a number of ways. In one embodiment, the estimated ground plane and the image areas corresponding to a clear path are overlaid. Image coordinates corresponding to a clear path, and image coordinates corresponding to a ground level in an estimated ground plane are used to define a clear path. In one embodiment of the clear path detection analysis, the estimated ground plane may be utilized in the above described likelihood analysis. The clear path confidence likelihood for each of the images areas are partially based upon an association with the estimated ground plane. The likelihood analysis evaluates image areas to assign a clear path confidence likelihood value. Classifiers may be used to increase or decrease the clear path confidence likelihood value based upon features identified in the image area. The estimated ground plane may be used as an additional classifier in accordance with the likelihood analysis set forth above to increase the clear path confidence likelihood of an image area when the image area corresponds to the estimated ground plane. Image areas with a clear path confidence likelihood greater than a threshold confidence likelihood are defined as clear path.

The clear path detection analysis may also be used to augment and refine the ground plane estimation analysis. Image coordinates defined as clear by the clear path detection analysis may be incorporated in the estimated ground plane. Image coordinates not included in the estimated ground plane that the clear path detection has defined as clear are incorporated into the estimated ground plane, thereby expanding the estimated ground plane.

The image areas categorized into the snow elevation categories are used to enhance or refine image areas corresponding to the clear path identified by the clear path detection analysis. The image area can be used in a number of ways. In one embodiment, image areas identified as clear by the snow elevation change analysis are incorporated into image coordinates defined as clear by the clear path detection analysis. Image areas identified as not clear by the snow elevation change analysis can be excluded or subtracted from image coordinates defined as clear by the clear path detection analysis.

In another embodiment, image areas identified as clear and not clear by the snow elevation change analysis may be evaluated using the likelihood analysis described hereinabove. Image areas identified as clear by the snow elevation change analysis may increase the clear path confidence likelihood of the image area. Similarly, image areas identified as not clear by the snow elevation change analysis may decrease the clear path confidence likelihood of the image area.

Image areas associated with the snow elevation change category can be used in the clear path detection analysis. In one embodiment, image areas identified as a road surface between two transitional areas by the snow elevation change analysis increase the clear path confidence likelihood value associated with a corresponding image area using the clear path detection analysis. Additionally, detected vehicle tracks can additionally be incorporated into or overlaid with the texture-rich and textureless pixel-based clear path detection methods and analytically utilized to reinforce the location of a clear path. Vehicle tracks can similarly be utilized to reinforce a ground level in a texture-rich map. In an embodiment utilizing segmentation of the image into areas capable of representing a clear path from areas not capable of representing a clear path, image areas identified as a boundary by the snow elevation change analysis are used to focus the clear path detection analysis on image area between identified boundaries thereby increasing computational efficiency.

It will be appreciated that ground plane estimation and snow elevation change analysis are performed iteratively as a vehicle travels down the road. A section of roadway or proposed clear path will be analyzed a number of times as the vehicle approaches. Confidence in the section of the roadway can be built over the iterative analyses and improved over a single analysis. However, it will be appreciated that traffic flow and other factors can change the conditions of the roadway as the vehicle travels. Methods known in the art can be used to distinguish between noise in the analyses falsely indicating a not clear path versus changing conditions on the roadway actually indicating a not clear condition.

Step 808 of FIG. 16 illustrates mutual benefits refinement, inputting a clear path and topographical variation analysis information, depicted as exemplary ground plane estimation, to output an enhanced clear path. As will be appreciated from the above described methods, clear path can benefit from detection of topographical variation analysis, augmenting an understanding of what areas are likely to be a clear path. It will be appreciated that enhanced topographical variation analysis can similarly be accomplished by analysis of the identified clear path. For example, on a snowy road, boundaries described by the clear path detection can be used to adjust thresholds utilized to estimate snow elevation, as described above. Such an analysis can be iteratively reinforced with subsequent images, building confidence along the route of travel of both the clear path and the properties or factors affecting snow detection. Additionally, a single image can be iteratively examined, with multiple iterations of clear path analysis and snow elevation analysis reinforcing use of the single image. Such an analysis loop can beneficially refine starting assumptions and results of the analyses. Similarly, ground plane estimation can be benefited by use of clear path analysis, utilizing the clear path as a reinforcement or starting point in the LIDAR returns for the ground plane. In snow covered road circumstances, the additional variability of the snow can be taken into account in defining the ground plane, and the existence of the ground plane can be reinforced by overlaying the presence of the detected clear path to indicate that the ground plane is correctly identified. FIG. 17 graphically depicts such an iterative analysis, in accordance with the present disclosure. Step 808 is depicted, including topographical variation analysis refinement in step 805 and clear path refinement in step 807. Step 808 outputs both the enhanced clear path, as described above, and additionally exemplary enhanced ground plane estimation information.

Ground plane estimation and snow elevation detection can be operated at the same time and can each be used to mutually reinforce clear path in unison. FIG. 14 graphically depicts exemplary operation of clear path analysis, snow elevation detection, and ground plane estimation, in accordance with the present disclosure. Method 900 begins at step 902, wherein images are generated and analyzed through snow elevation detection at step 904 and clear path analysis at step 906, according to methods described herein. Similarly, LIDAR is utilized for ground plane estimation in step 908. Outputs from the three analysis methods of steps 904, 906, and 908 are combined for mutual benefit analysis in step 910, and enhanced snow elevation, enhanced ground plane estimation and enhanced clear path are outputs of step 910. It will be appreciated that other similar methods described above or known in the art can further or alternatively be applied to the mutual benefit refinement for enhancement of the related methods.

Methods above describe utilizing an image or images from a camera to perform clear path detection analysis, for example, by the patch-based method. Additional methods describe utilizing an image or images from a camera utilizing a topographical variation analysis in a method to augment or enhance the clear path. It will be appreciated that a single camera may be used to generate an image or images for use simultaneously for both exemplary methods. However, it will also be appreciated that a plurality of cameras selected based upon the individual methods employed may be used to provide dedicated or enhanced images to each of the methods employed. Additionally, it will be appreciated that a camera or a plurality of cameras can be used in combination with a radar, LIDAR, ultrasonic, digital map, communications device or other device.

As mentioned above, processing module 120 may include algorithms and mechanisms to actuate autonomous driving control by means known in the art and not described herein, or processing module 120 may simply provide information to a separate autonomous driving system. Reactions to perceived objects can vary, and include but are not limited to steering changes, throttle changes, braking responses, and warning and relinquishing control of the vehicle to the operator.

The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims. 

1. Method for detecting a clear path of travel for a vehicle, the detecting comprising a fusion of a plurality of analyses, the method comprising: monitoring an image from a camera device; analyzing the image through clear path detection analysis to determine a clear path of travel within the image; analyzing an area in front of the vehicle utilizing a topographical variation analysis to determine a flat surface upon which the vehicle can travel; combining the clear path of travel and the determined flat surface to describe an enhanced clear path of travel; and utilizing the enhanced clear path of travel to navigate the vehicle.
 2. The method of claim 1, wherein analyzing the area in front of the vehicle comprises utilizing ground plane estimation analysis.
 3. The method of claim 2, wherein utilizing ground plane estimation analysis comprises utilizing a plurality of images to estimate heights of visible features in front of the vehicle based upon relative movement of features between the plurality of images.
 4. The method of claim 2, wherein utilizing ground plane estimation analysis comprises utilizing a LIDAR device to determine a ground plane estimate in front of the vehicle.
 5. The method of claim 1, wherein analyzing the area in front of the vehicle comprises utilizing snow elevation change analysis.
 6. The method of claim 5, wherein the snow elevation change analysis comprises analyzing an image based upon a frequency of pixel change to estimate the flat surface.
 7. The method of claim 6, wherein analyzing the image based upon the frequency of pixel change to estimate the flat surface comprises analyzing a change in pixel intensity.
 8. The method of claim 6, wherein analyzing the image based upon the frequency of pixel change to estimate the flat surface comprises analyzing a change in pixel color.
 9. The method of claim 6, wherein analyzing the image based upon the frequency of pixel change to estimate the flat surface comprises identifying a boundary to the flat surface based upon identifying an area of large pixel change in excess of a threshold.
 10. The method of claim 9, wherein analyzing the image based upon the frequency of pixel change to estimate the flat surface further comprises identifying the flat surface based upon identifying an area adjacent to the boundary of moderate pixel change less than the threshold and greater than a lower threshold.
 11. The method of claim 6, wherein analyzing the image based upon the frequency of pixel change to estimate the flat surface comprises identifying boundaries upon both sides of the flat surface based upon identifying areas of large pixel change in excess of a threshold.
 12. The method of claim 11, wherein analyzing the image based upon the frequency of pixel change to estimate the flat surface further comprises identifying the flat surface based upon identifying an area between the boundaries of moderate pixel change less than the threshold and greater than a lower threshold.
 13. The method of claim 1, wherein analyzing the image through clear path detection analysis comprises utilizing an analysis selected from the group consisting of a patch-based analysis, a pixel-based analysis, a segmentation-based analysis, and an example-based analysis.
 14. The method of claim 1, wherein analyzing the image through clear path detection analysis comprises utilizing a fusion of analyses selected from the group consisting of a patch-based analysis, a pixel-based analysis, a segmentation-based analysis, and an example-based analysis.
 15. The method of claim 1, further comprising iteratively analyzing the area in front of the vehicle utilizing the topographical variation analysis to build confidence in the flat surface.
 16. The method of claim 1, wherein combining the clear path of travel and the determined flat surface to describe the enhanced clear path of travel comprises utilizing as the enhanced clear path only an area contained by both the clear path of travel and the determined flat surface.
 17. The method of claim 1, wherein combining the clear path of travel and the determined flat surface further describes an enhanced topographical variation analysis; and utilizing the enhanced topographical variation analysis to navigate the vehicle.
 18. The method of claim 1, wherein the topographical variation analysis comprises ground plane estimation and snow elevation detection.
 19. A system for detecting a clear path of travel for a vehicle, the detecting comprising a fusion of a plurality of analyses, the system comprising: a camera device; and a processing module monitor images from the camera device, and analyzing the images comprising determining a clear path of travel from other portions of the image that do not indicate a clear path of travel, and monitoring data describing topography in front of the vehicle, analyzing the data describing the topography in front of the vehicle, analyzing the clear path and the analysis of the data describing the topography in front of the vehicle, modifying the clear path based upon the analysis of the clear path and the analysis of the data describing the topography in front of the vehicle, and aiding navigation of the vehicle based upon the modified clear path.
 20. The system of claim 19, further comprising an autonomous steering system, wherein the autonomous steering system utilizes the navigation aid from the processing module. 